The present invention relates to a flexible board connector for electrically connecting a flexible board to a circuit board and to a connection structure of a flexible board to a circuit board.
In recent years, electronic devices of portable telephones, video cameras and so on have been promoted reducing their size and weight while internally included many built-in electronic components. Many of the electronic components have leads and terminals electrically connected with solder to component mounting lands arranged on a circuit board. In portable telephones, of which the size reduction has been promoted, even comparatively large components such as LCD modules and keypads are arranged on a circuit board, and a plurality of such circuit boards are normally employed. In order to electrically connect the plurality of circuit boards with one another, many flexible boards are employed. Moreover, flexible boards are employed to electrically connect other parts of camera modules and so on to the circuit board. Such a flexible board is sometimes required to be connected from the lower surface side of the circuit board to the connector arranged together with the electronic components on the upper surface of the circuit board due to restrictions in design.
Conventionally, the following connection structures have been adopted in order to connect the flexible boards to the connectors of the circuit board from the lower surface side.
(1) As shown in FIG. 9, a circuit board 52, on the upper surface of which an electronic component 51 is arranged, is provided with a connector 53 on its upper surface and a through hole 52a. A flexible board 54 is guided from the lower surface side to the upper surface side of the circuit board 52 via the through hole 52a, and the connection portion of the flexible board 54 is connected to the connector 53.
(2) As shown in FIG. 10, a connector 63 is provided in the neighborhood of an edge portion of the circuit board 62 on the upper surface of which the electronic components 61 are arranged, and the connection portion of the flexible board 64 is connected to the connector 63 by bending the flexible board 64 so that the board covers the edge portion from the lower surface side of the circuit board 62.
(3) As shown in FIG. 11, a connector 73 is provided on the lower surface of a circuit board 72 on the upper surface of which the electronic components 71 are arranged, and a flexible board 74 on the lower surface side is connected to the connector 73 without being guided to the upper surface side.
Some of the conventional connectors 53, 63 and 73 hold and fix the connection portion of the flexible board between a base part fixed to the circuit board and a pivot part pivotally connected to the base part. Moreover, there is a connector, which is fixed to a circuit board, includes an engagement pawl and a contact terminal, engages the engagement pawl with an engagement hole of a flexible board and electrically connects the contact terminal to the connection terminal of the flexible board (refer to JP H09-22760).
However, the connection structure of the flexible board to the circuit board of the item (1) has a problem that, if the flexible board 54, which passed through the through hole 52a, receives vibrations or impact while being brought in contact with the edge of the through hole 52a, the wiring formed on the flexible board 54 is cut by the edge. As a method for solving the above problem, it can be considered to chamfer the edge of the through hole 52a, to arrange a cover to cover the edge, and to use a jig for shaping the flexible board 54 into a shape such that the board does not come in contact with the edge or the like. However, each of the methods has the problem of causing a cost increase. Moreover, the connection structure of the flexible board to the circuit board of the item (2) has a problem that restrictions on the circuit design increase since the connector 63 needs to be arranged at the edge portion of the circuit board 52 in addition to a problem similar to that of the item (1). There is a further problem that the total length of the flexible board 64 becomes long. The connection structure of the flexible board to the circuit board of the item (3) has a problem that the cost is increased further than when the electronic components and the connector are arranged on the upper surface since a wiring for the connector 73 also needs to be arranged on the lower surface despite that the electronic component 71 is arranged only on the upper surface of the circuit board 72.
What is particularly important to the electronic devices, of which the reductions in size and weight have been promoted, is a reduction in thickness. Therefore, in accordance with the reductions in size and thickness of electronic components and so on, the connectors for flexible boards are also demanded to be reduced in size and thickness.
However, the connectors 53, 63 and 73 of the items (1), (2) and (3), which are employed for the connection structure of the flexible board to the circuit board, have conventionally been arranged on the upper surface or the lower surface of the circuit boards 52, 62 and 72. Therefore, all of the connectors 53, 63 and 73 are to project from the surfaces of the circuit boards 52, 62 and 72. This therefore leads to a problem that the circuit boards 52, 62 and 72 and the flexible boards 54, 64 and 74 in the mutually connected state come to have a comparatively great thickness. It can be considered to reduce the thickness of the components of insulators, terminals and so on included in the connectors 53, 63 and 73 in order to reduce the thickness of the connectors 53, 63 and 73. However, this disadvantageously causes a reduction in structural strength, defective connection and so on.